| Calamites, Sphenophyllum, Pecopteris, Neuropteris, Alethopteris|
Annularia is a plant fossil belonging to the order Equisetales.
Annularia is a form taxon. It is the name given to Calamites leaves. In fact the stems and the radiating structures of the leaf whorls is similar in the Calamites, an extinct genus of horsetails.
These horsetails, belonging to the class of Sphenopsida, were arborescent and grew to a height of 32 feet (10 meters) in a tree-like form.
Annularia leaves are arranged in whorls of between 8-13 leaves. Its shape is quite variable, being oval in Annularia sphenophylloides and between linear and lanceolate in Annularia radiata, but they are always flat and of varying lengths.
Fossils of this genus have been discovered in the Permian strata of Russia and in the Carboniferous (around 360 to 300 million years ago) strata of the United States, Canada, China and Europe.